The present invention resides in a cutter drive in which rotary motion derived from a rotary drive source is translated into reciprocating linear motion driving an elongate knife through a given stroke to cut patterns in a ply or a stack of plies of sheet material, and more particularly relates to a vibration dampening system employed in the cutter drive in which means are provided for dynamically balancing the full mass of the reciprocating knife and any associated connecting linkage without creating uncompensated lateral forces.
In known machines for cutting sheet material spread on a supporting surface, an elongate knife is eccentrically connected to a rotating flywheel to effect reciprocation of the knife when the flywheel is rotated. An example of one such type of eccentric drive arrangement for reciprocating a knife is disclosed in U.S. Pat. No. 4,048,891 issued on Sept. 20, 1977 to Pearl which, patent being commonly assigned with the assignee of the present invention and being hereby incorporated by reference. In this patent, a swivel device linking the flywheel with the knife is employed to effect controlled rotation of the knife about its axis of reciprocation in order that the leading edge be made to follow given a path along which the material is to be cut. To do this however, it is necessary that the swivel linkage as well as the knife together be reciprocated by the eccentric drive. Although this arrangement has proven to be a very effective means for guiding the knife along a designated path, it has been found that the reciprocated mass constituted by the knife and the swivel device, or even the knife alone, generates undersirable vibrations when the flywheel rotates at a high speed, for example at about 5200 revolutions per minute. These vibrations may detrimentally affect the accuracy of a control resolver positioned adjacent the knife generating feedback signals to a controller which may in turn alter the cutting path of the blade as necessary to compensate for any detected deviation from a predetermined cutting parameter. In addition, these vibrations wear and loosen otherwise rigidly connected parts on the cutting machine thus requiring additional maintenance which otherwise would not be necessary. Also, when the flywheel is rotated at high speeds, the vibrations caused by the reciprocating mass generates high noise levels in the surrounding work environment.
Hitherto, attempts have been made to reduce the vibrations caused by the reciprocating knife assembly by offsetting the reciprocated mass by placing a counterweight on the flywheel located diametrically oppositely of the connecting point between the knife linkage and the pulley. While such a measure has proven to be partially effective in compensating for the reciprocating mass, its effectiveness to fully compensate for the reciprocated load is nevertheless limited by the lateral forces introduced into the system when the counterweight moves from top dead center to bottom dead center and vice versa in its rotation. Due to these lateral or side-to-side dynamic forces, the offsetting mass of the counterweight could never be more than a percentage, usually on the order of 50 percent, of the total reciprocated mass constituted by the reciprocating knife and its associated eccentric mounting connection.
In accordance with the invention, a cutter drive vibrational dampening system is provided wherein the substantially entire mass of the reciprocating knife and its associated eccentric connection is compensated for without introducing additional lateral forces to the cutter head and system supporting it.
A further object of the invention is to provide a dynamically balanced drive system which reduces the operating noise level of a cutter head as well as reducing the amount of wear to the head and its associated component parts.
Yet, a further object of the present invention is to provide a dynamically balanced drive system in which both vertical and horizontal forces are balanced at various rotational velocities.
Other objects and features of the invention will become apparent from the disclosure and the appended claims.